Contract Source Code:
// SPDX-License-Identifier: MIT
//http://www.crypto20.tech/
pragma solidity =0.8.15;
import "@openzeppelin/contracts/utils/Context.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
interface IPair {
function getReserves() external view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);
function token0() external view returns (address);
}
interface IFactory{
function createPair(address tokenA, address tokenB) external returns (address pair);
function getPair(address tokenA, address tokenB) external view returns (address pair);
}
interface IRouter {
function factory() external pure returns (address);
function WETH() external pure returns (address);
function addLiquidityETH(
address token,
uint amountTokenDesired,
uint amountTokenMin,
uint amountETHMin,
address to,
uint deadline
) external payable returns (uint amountToken, uint amountETH, uint liquidity);
function swapExactTokensForTokensSupportingFeeOnTransferTokens(
uint amountIn,
uint amountOutMin,
address[] calldata path,
address to,
uint deadline
) external;
function swapExactETHForTokens(uint amountOutMin, address[] calldata path, address to, uint deadline)
external
payable
returns (uint[] memory amounts);
function swapExactTokensForETHSupportingFeeOnTransferTokens(
uint amountIn,
uint amountOutMin,
address[] calldata path,
address to,
uint deadline) external;
}
contract Crypto20 is ERC20, Ownable {
IRouter public router;
address public pair;
address public devWallet;
uint256 public swapTokensAtAmount;
uint256 public maxBuyAmount;
uint256 public maxSellAmount;
uint256 public maxWallet;
mapping(address => bool) public _isBot;
mapping(address => bool) private _isExcludedFromFees;
mapping(address => bool) private _isExcludedFromMaxWallet;
mapping(address => bool) public automatedMarketMakerPairs;
bool private swapping;
bool public swapEnabled = true;
bool public tradingEnabled;
event ExcludeFromFees(address indexed account, bool isExcluded);
event ExcludeMultipleAccountsFromFees(address[] accounts, bool isExcluded);
event SetAutomatedMarketMakerPair(address indexed pair, bool indexed value);
struct Taxes {
uint256 dev;
}
Taxes public buyTaxes = Taxes(0);
Taxes public sellTaxes = Taxes(0);
uint256 public totalBuyTax = 10;
uint256 public totalSellTax = 10;
constructor(address _dev)
ERC20("Crypto 2.0", "2.0")
{
setSwapTokensAtAmount(300000);
updateMaxWalletAmount(2000000);
setMaxBuyAndSell(2000000, 2000000);
setDevWallet(_dev);
IRouter _router = IRouter(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D);
address _pair = IFactory(_router.factory()).createPair(
address(this),
_router.WETH()
);
router = _router;
pair = _pair;
excludeFromFees(owner(), true);
excludeFromFees(address(this), true);
excludeFromMaxWallet(_pair, true);
excludeFromMaxWallet(address(this), true);
excludeFromMaxWallet(address(_router), true);
_setAutomatedMarketMakerPair(_pair, true);
_mint(owner(), 100000000 * (10**18));
}
receive() external payable {}
function excludeFromFees(address account, bool excluded)
public
onlyOwner
{
require(
_isExcludedFromFees[account] != excluded,
" Account is already the value of 'excluded'"
);
_isExcludedFromFees[account] = excluded;
emit ExcludeFromFees(account, excluded);
}
function excludeFromMaxWallet(address account, bool excluded)
public
onlyOwner
{
_isExcludedFromMaxWallet[account] = excluded;
}
function excludeMultipleAccountsFromFees(
address[] calldata accounts,
bool excluded
) public onlyOwner {
for (uint256 i = 0; i < accounts.length; i++) {
_isExcludedFromFees[accounts[i]] = excluded;
}
emit ExcludeMultipleAccountsFromFees(accounts, excluded);
}
function setBuyTaxes( uint256 _dev) external onlyOwner{
require(_dev <= 20, "Fee must be <= 20%");
buyTaxes = Taxes( _dev);
totalBuyTax = _dev;
}
function setSellTaxes(uint256 _dev) external onlyOwner{
require( _dev <= 20, "Fee must be <= 20%");
sellTaxes = Taxes( _dev);
totalSellTax = _dev;
}
function setDevWallet(address newWallet) public onlyOwner {
devWallet = newWallet;
}
function updateMaxWalletAmount(uint256 newNum) public onlyOwner {
require(newNum >= 1000000, "Cannot set maxWallet lower than 1%");
maxWallet = newNum * (10**18);
}
function setMaxBuyAndSell(uint256 maxBuy, uint256 maxSell)
public
onlyOwner
{
require(maxBuy >= 1000000, "Cannot set maxbuy lower than 1% ");
require(maxSell >= 500000, "Cannot set maxsell lower than 0.5% ");
maxBuyAmount = maxBuy * 10**18;
maxSellAmount = maxSell * 10**18;
}
function setSwapTokensAtAmount(uint256 amount) public onlyOwner {
swapTokensAtAmount = amount * 10**18;
}
function setSwapEnabled(bool _enabled) external onlyOwner {
swapEnabled = _enabled;
}
function rescueETH20Tokens(address tokenAddress) external onlyOwner {
IERC20(tokenAddress).transfer(
owner(),
IERC20(tokenAddress).balanceOf(address(this))
);
}
function forceSend() external onlyOwner {
(bool success, ) = payable(devWallet).call{
value: address(this).balance
}("");
require(success, "Failed to send Ether to dev wallet");
}
function updateRouter(address newRouter) external onlyOwner {
router = IRouter(newRouter);
}
function activateTrading() external onlyOwner {
require(!tradingEnabled, "Trading enabled");
tradingEnabled = true;
}
function setBot(address bot, bool value) external onlyOwner {
require(_isBot[bot] != value);
_isBot[bot] = value;
}
function setBulkBot(address[] memory bots, bool value) external onlyOwner {
for (uint256 i; i < bots.length; i++) {
_isBot[bots[i]] = value;
}
}
function setAutomatedMarketMakerPair(address newPair, bool value)
external
onlyOwner
{
_setAutomatedMarketMakerPair(newPair, value);
}
function _setAutomatedMarketMakerPair(address newPair, bool value) private {
require(
automatedMarketMakerPairs[newPair] != value,
"Automated market maker pair is already set to that value"
);
automatedMarketMakerPairs[newPair] = value;
emit SetAutomatedMarketMakerPair(newPair, value);
}
function isExcludedFromFees(address account) public view returns (bool) {
return _isExcludedFromFees[account];
}
function _transfer(
address from,
address to,
uint256 amount
) internal override {
require(from != address(0), "ERC20: transfer from the zero address");
require(to != address(0), "ERC20: transfer to the zero address");
require(!_isBot[from] && !_isBot[to], "Bye Bot");
if (
!_isExcludedFromFees[from] && !_isExcludedFromFees[to] && !swapping
) {
require(tradingEnabled, "Trading not active");
if (automatedMarketMakerPairs[to]) {
require(
amount <= maxSellAmount,
"You are exceeding maxSellAmount"
);
} else if (automatedMarketMakerPairs[from])
require(
amount <= maxBuyAmount,
"You are exceeding maxBuyAmount"
);
if (!_isExcludedFromMaxWallet[to]) {
require(
amount + balanceOf(to) <= maxWallet,
"Unable to exceed Max Wallet"
);
}
}
if (amount == 0) {
super._transfer(from, to, 0);
return;
}
uint256 contractTokenBalance = balanceOf(address(this));
bool canSwap = contractTokenBalance >= swapTokensAtAmount;
if (
canSwap &&
!swapping &&
swapEnabled &&
automatedMarketMakerPairs[to] &&
!_isExcludedFromFees[from] &&
!_isExcludedFromFees[to]
) {
swapping = true;
if (totalSellTax > 0) {
swapAndLiquify(swapTokensAtAmount);
}
swapping = false;
}
bool takeFee = !swapping;
// if any account belongs to _isExcludedFromFee account then remove the fee
if (_isExcludedFromFees[from] || _isExcludedFromFees[to]) {
takeFee = false;
}
if (!automatedMarketMakerPairs[to] && !automatedMarketMakerPairs[from])
takeFee = false;
if (takeFee) {
uint256 feeAmt;
if (automatedMarketMakerPairs[to])
feeAmt = (amount * totalSellTax) / 100;
else if (automatedMarketMakerPairs[from])
feeAmt = (amount * totalBuyTax) / 100;
amount = amount - feeAmt;
super._transfer(from, address(this), feeAmt);
}
super._transfer(from, to, amount);
}
function swapAndLiquify(uint256 tokens) private {
uint256 toSwap = tokens;
swapTokensForETH(toSwap);
uint256 contractrewardbalance = address(this).balance;
uint256 devAmt = contractrewardbalance ;
if (devAmt > 0) {
(bool success, ) = payable(devWallet).call{value: devAmt}("");
require(success, "Failed to send Ether to dev wallet");
}
}
function swapTokensForETH(uint256 tokenAmount) private {
address[] memory path = new address[](2);
path[0] = address(this);
path[1] = router.WETH();
_approve(address(this), address(router), tokenAmount);
router.swapExactTokensForETHSupportingFeeOnTransferTokens(
tokenAmount,
0,
path,
address(this),
block.timestamp
);
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/ERC20.sol)
pragma solidity ^0.8.0;
import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.sol";
/**
* @dev Implementation of the {IERC20} interface.
*
* This implementation is agnostic to the way tokens are created. This means
* that a supply mechanism has to be added in a derived contract using {_mint}.
* For a generic mechanism see {ERC20PresetMinterPauser}.
*
* TIP: For a detailed writeup see our guide
* https://forum.openzeppelin.com/t/how-to-implement-erc20-supply-mechanisms/226[How
* to implement supply mechanisms].
*
* The default value of {decimals} is 18. To change this, you should override
* this function so it returns a different value.
*
* We have followed general OpenZeppelin Contracts guidelines: functions revert
* instead returning `false` on failure. This behavior is nonetheless
* conventional and does not conflict with the expectations of ERC20
* applications.
*
* Additionally, an {Approval} event is emitted on calls to {transferFrom}.
* This allows applications to reconstruct the allowance for all accounts just
* by listening to said events. Other implementations of the EIP may not emit
* these events, as it isn't required by the specification.
*
* Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
* functions have been added to mitigate the well-known issues around setting
* allowances. See {IERC20-approve}.
*/
contract ERC20 is Context, IERC20, IERC20Metadata {
mapping(address => uint256) private _balances;
mapping(address => mapping(address => uint256)) private _allowances;
uint256 private _totalSupply;
string private _name;
string private _symbol;
/**
* @dev Sets the values for {name} and {symbol}.
*
* All two of these values are immutable: they can only be set once during
* construction.
*/
constructor(string memory name_, string memory symbol_) {
_name = name_;
_symbol = symbol_;
}
/**
* @dev Returns the name of the token.
*/
function name() public view virtual override returns (string memory) {
return _name;
}
/**
* @dev Returns the symbol of the token, usually a shorter version of the
* name.
*/
function symbol() public view virtual override returns (string memory) {
return _symbol;
}
/**
* @dev Returns the number of decimals used to get its user representation.
* For example, if `decimals` equals `2`, a balance of `505` tokens should
* be displayed to a user as `5.05` (`505 / 10 ** 2`).
*
* Tokens usually opt for a value of 18, imitating the relationship between
* Ether and Wei. This is the default value returned by this function, unless
* it's overridden.
*
* NOTE: This information is only used for _display_ purposes: it in
* no way affects any of the arithmetic of the contract, including
* {IERC20-balanceOf} and {IERC20-transfer}.
*/
function decimals() public view virtual override returns (uint8) {
return 18;
}
/**
* @dev See {IERC20-totalSupply}.
*/
function totalSupply() public view virtual override returns (uint256) {
return _totalSupply;
}
/**
* @dev See {IERC20-balanceOf}.
*/
function balanceOf(address account) public view virtual override returns (uint256) {
return _balances[account];
}
/**
* @dev See {IERC20-transfer}.
*
* Requirements:
*
* - `to` cannot be the zero address.
* - the caller must have a balance of at least `amount`.
*/
function transfer(address to, uint256 amount) public virtual override returns (bool) {
address owner = _msgSender();
_transfer(owner, to, amount);
return true;
}
/**
* @dev See {IERC20-allowance}.
*/
function allowance(address owner, address spender) public view virtual override returns (uint256) {
return _allowances[owner][spender];
}
/**
* @dev See {IERC20-approve}.
*
* NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
* `transferFrom`. This is semantically equivalent to an infinite approval.
*
* Requirements:
*
* - `spender` cannot be the zero address.
*/
function approve(address spender, uint256 amount) public virtual override returns (bool) {
address owner = _msgSender();
_approve(owner, spender, amount);
return true;
}
/**
* @dev See {IERC20-transferFrom}.
*
* Emits an {Approval} event indicating the updated allowance. This is not
* required by the EIP. See the note at the beginning of {ERC20}.
*
* NOTE: Does not update the allowance if the current allowance
* is the maximum `uint256`.
*
* Requirements:
*
* - `from` and `to` cannot be the zero address.
* - `from` must have a balance of at least `amount`.
* - the caller must have allowance for ``from``'s tokens of at least
* `amount`.
*/
function transferFrom(address from, address to, uint256 amount) public virtual override returns (bool) {
address spender = _msgSender();
_spendAllowance(from, spender, amount);
_transfer(from, to, amount);
return true;
}
/**
* @dev Atomically increases the allowance granted to `spender` by the caller.
*
* This is an alternative to {approve} that can be used as a mitigation for
* problems described in {IERC20-approve}.
*
* Emits an {Approval} event indicating the updated allowance.
*
* Requirements:
*
* - `spender` cannot be the zero address.
*/
function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
address owner = _msgSender();
_approve(owner, spender, allowance(owner, spender) + addedValue);
return true;
}
/**
* @dev Atomically decreases the allowance granted to `spender` by the caller.
*
* This is an alternative to {approve} that can be used as a mitigation for
* problems described in {IERC20-approve}.
*
* Emits an {Approval} event indicating the updated allowance.
*
* Requirements:
*
* - `spender` cannot be the zero address.
* - `spender` must have allowance for the caller of at least
* `subtractedValue`.
*/
function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
address owner = _msgSender();
uint256 currentAllowance = allowance(owner, spender);
require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
unchecked {
_approve(owner, spender, currentAllowance - subtractedValue);
}
return true;
}
/**
* @dev Moves `amount` of tokens from `from` to `to`.
*
* This internal function is equivalent to {transfer}, and can be used to
* e.g. implement automatic token fees, slashing mechanisms, etc.
*
* Emits a {Transfer} event.
*
* Requirements:
*
* - `from` cannot be the zero address.
* - `to` cannot be the zero address.
* - `from` must have a balance of at least `amount`.
*/
function _transfer(address from, address to, uint256 amount) internal virtual {
require(from != address(0), "ERC20: transfer from the zero address");
require(to != address(0), "ERC20: transfer to the zero address");
_beforeTokenTransfer(from, to, amount);
uint256 fromBalance = _balances[from];
require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
unchecked {
_balances[from] = fromBalance - amount;
// Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
// decrementing then incrementing.
_balances[to] += amount;
}
emit Transfer(from, to, amount);
_afterTokenTransfer(from, to, amount);
}
/** @dev Creates `amount` tokens and assigns them to `account`, increasing
* the total supply.
*
* Emits a {Transfer} event with `from` set to the zero address.
*
* Requirements:
*
* - `account` cannot be the zero address.
*/
function _mint(address account, uint256 amount) internal virtual {
require(account != address(0), "ERC20: mint to the zero address");
_beforeTokenTransfer(address(0), account, amount);
_totalSupply += amount;
unchecked {
// Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
_balances[account] += amount;
}
emit Transfer(address(0), account, amount);
_afterTokenTransfer(address(0), account, amount);
}
/**
* @dev Destroys `amount` tokens from `account`, reducing the
* total supply.
*
* Emits a {Transfer} event with `to` set to the zero address.
*
* Requirements:
*
* - `account` cannot be the zero address.
* - `account` must have at least `amount` tokens.
*/
function _burn(address account, uint256 amount) internal virtual {
require(account != address(0), "ERC20: burn from the zero address");
_beforeTokenTransfer(account, address(0), amount);
uint256 accountBalance = _balances[account];
require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
unchecked {
_balances[account] = accountBalance - amount;
// Overflow not possible: amount <= accountBalance <= totalSupply.
_totalSupply -= amount;
}
emit Transfer(account, address(0), amount);
_afterTokenTransfer(account, address(0), amount);
}
/**
* @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
*
* This internal function is equivalent to `approve`, and can be used to
* e.g. set automatic allowances for certain subsystems, etc.
*
* Emits an {Approval} event.
*
* Requirements:
*
* - `owner` cannot be the zero address.
* - `spender` cannot be the zero address.
*/
function _approve(address owner, address spender, uint256 amount) internal virtual {
require(owner != address(0), "ERC20: approve from the zero address");
require(spender != address(0), "ERC20: approve to the zero address");
_allowances[owner][spender] = amount;
emit Approval(owner, spender, amount);
}
/**
* @dev Updates `owner` s allowance for `spender` based on spent `amount`.
*
* Does not update the allowance amount in case of infinite allowance.
* Revert if not enough allowance is available.
*
* Might emit an {Approval} event.
*/
function _spendAllowance(address owner, address spender, uint256 amount) internal virtual {
uint256 currentAllowance = allowance(owner, spender);
if (currentAllowance != type(uint256).max) {
require(currentAllowance >= amount, "ERC20: insufficient allowance");
unchecked {
_approve(owner, spender, currentAllowance - amount);
}
}
}
/**
* @dev Hook that is called before any transfer of tokens. This includes
* minting and burning.
*
* Calling conditions:
*
* - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
* will be transferred to `to`.
* - when `from` is zero, `amount` tokens will be minted for `to`.
* - when `to` is zero, `amount` of ``from``'s tokens will be burned.
* - `from` and `to` are never both zero.
*
* To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
*/
function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual {}
/**
* @dev Hook that is called after any transfer of tokens. This includes
* minting and burning.
*
* Calling conditions:
*
* - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
* has been transferred to `to`.
* - when `from` is zero, `amount` tokens have been minted for `to`.
* - when `to` is zero, `amount` of ``from``'s tokens have been burned.
* - `from` and `to` are never both zero.
*
* To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
*/
function _afterTokenTransfer(address from, address to, uint256 amount) internal virtual {}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (access/Ownable.sol)
pragma solidity ^0.8.0;
import "../utils/Context.sol";
/**
* @dev Contract module which provides a basic access control mechanism, where
* there is an account (an owner) that can be granted exclusive access to
* specific functions.
*
* By default, the owner account will be the one that deploys the contract. This
* can later be changed with {transferOwnership}.
*
* This module is used through inheritance. It will make available the modifier
* `onlyOwner`, which can be applied to your functions to restrict their use to
* the owner.
*/
abstract contract Ownable is Context {
address private _owner;
event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
/**
* @dev Initializes the contract setting the deployer as the initial owner.
*/
constructor() {
_transferOwnership(_msgSender());
}
/**
* @dev Throws if called by any account other than the owner.
*/
modifier onlyOwner() {
_checkOwner();
_;
}
/**
* @dev Returns the address of the current owner.
*/
function owner() public view virtual returns (address) {
return _owner;
}
/**
* @dev Throws if the sender is not the owner.
*/
function _checkOwner() internal view virtual {
require(owner() == _msgSender(), "Ownable: caller is not the owner");
}
/**
* @dev Leaves the contract without owner. It will not be possible to call
* `onlyOwner` functions. Can only be called by the current owner.
*
* NOTE: Renouncing ownership will leave the contract without an owner,
* thereby disabling any functionality that is only available to the owner.
*/
function renounceOwnership() public virtual onlyOwner {
_transferOwnership(address(0));
}
/**
* @dev Transfers ownership of the contract to a new account (`newOwner`).
* Can only be called by the current owner.
*/
function transferOwnership(address newOwner) public virtual onlyOwner {
require(newOwner != address(0), "Ownable: new owner is the zero address");
_transferOwnership(newOwner);
}
/**
* @dev Transfers ownership of the contract to a new account (`newOwner`).
* Internal function without access restriction.
*/
function _transferOwnership(address newOwner) internal virtual {
address oldOwner = _owner;
_owner = newOwner;
emit OwnershipTransferred(oldOwner, newOwner);
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)
pragma solidity ^0.8.0;
/**
* @dev Provides information about the current execution context, including the
* sender of the transaction and its data. While these are generally available
* via msg.sender and msg.data, they should not be accessed in such a direct
* manner, since when dealing with meta-transactions the account sending and
* paying for execution may not be the actual sender (as far as an application
* is concerned).
*
* This contract is only required for intermediate, library-like contracts.
*/
abstract contract Context {
function _msgSender() internal view virtual returns (address) {
return msg.sender;
}
function _msgData() internal view virtual returns (bytes calldata) {
return msg.data;
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)
pragma solidity ^0.8.0;
import "../IERC20.sol";
/**
* @dev Interface for the optional metadata functions from the ERC20 standard.
*
* _Available since v4.1._
*/
interface IERC20Metadata is IERC20 {
/**
* @dev Returns the name of the token.
*/
function name() external view returns (string memory);
/**
* @dev Returns the symbol of the token.
*/
function symbol() external view returns (string memory);
/**
* @dev Returns the decimals places of the token.
*/
function decimals() external view returns (uint8);
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/IERC20.sol)
pragma solidity ^0.8.0;
/**
* @dev Interface of the ERC20 standard as defined in the EIP.
*/
interface IERC20 {
/**
* @dev Emitted when `value` tokens are moved from one account (`from`) to
* another (`to`).
*
* Note that `value` may be zero.
*/
event Transfer(address indexed from, address indexed to, uint256 value);
/**
* @dev Emitted when the allowance of a `spender` for an `owner` is set by
* a call to {approve}. `value` is the new allowance.
*/
event Approval(address indexed owner, address indexed spender, uint256 value);
/**
* @dev Returns the amount of tokens in existence.
*/
function totalSupply() external view returns (uint256);
/**
* @dev Returns the amount of tokens owned by `account`.
*/
function balanceOf(address account) external view returns (uint256);
/**
* @dev Moves `amount` tokens from the caller's account to `to`.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a {Transfer} event.
*/
function transfer(address to, uint256 amount) external returns (bool);
/**
* @dev Returns the remaining number of tokens that `spender` will be
* allowed to spend on behalf of `owner` through {transferFrom}. This is
* zero by default.
*
* This value changes when {approve} or {transferFrom} are called.
*/
function allowance(address owner, address spender) external view returns (uint256);
/**
* @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* IMPORTANT: Beware that changing an allowance with this method brings the risk
* that someone may use both the old and the new allowance by unfortunate
* transaction ordering. One possible solution to mitigate this race
* condition is to first reduce the spender's allowance to 0 and set the
* desired value afterwards:
* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
*
* Emits an {Approval} event.
*/
function approve(address spender, uint256 amount) external returns (bool);
/**
* @dev Moves `amount` tokens from `from` to `to` using the
* allowance mechanism. `amount` is then deducted from the caller's
* allowance.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a {Transfer} event.
*/
function transferFrom(address from, address to, uint256 amount) external returns (bool);
}